The present invention relates to a method of positioning a disk-shaped medium, which is capable of precisely positioning the disk-shaped medium on a rotary shaft.
A conventional method will be explained with reference to FIGS. 5A and 5B. FIG. 5A is an explanation view (a plan view) of a servo track writer and FIG. 5B is an explanation view (a sectional view) thereof, in each of which a plurality of disk-shaped media 10 have been set. A plurality of disk-shaped media 10 are piled to cover a hub 12 with regular separations and arranged in the axial direction of the hub 12. The hub 12 is connected to a motor 16 with a hub adaptor 14, and the hub 12 is rotated by the motor 16. With this structure, servo track data can be written on the disk-shaped media 10 by a writing head of a recording apparatus.
In the apparatus for writing servo track data on the disk-shaped media 10 which have been attached to the hub 12, centers of the disk-shaped media 10 must be correctly coincided with a rotational axis of the motor 16.
However, clearances must be formed between the disk-shaped media 10 and the hub 12 when the disk-shaped media 10 are set on the hub 12. Further, a clearance must be formed between the hub 12 and the hub adaptor 14 when the hub 12 is attached to the hub adaptor 14. Therefore, errors caused by the clearances must be removed so as to correctly coincide the centers of the disk-shaped media 10 with the rotational axis of the motor 16.
Conventionally, when the disk-shaped media 10 are attached to the hub 12, the disk-shaped media 10 are biased from the right so as to shift the centers of the disk-shaped media 10 leftward with respect to the center of the hub 12. On the other hand, when the hub 12 is attached to the hub adaptor 14, the hub is biased from the left so as to shift the center of the hub 12 rightward with respect to the center of the hub adaptor 14. With this method the clearances disappear and the centers of the disk-shaped media 10 can coincide with the center of the rotational axis of the motor 16.
In the conventional method, the centers of the disk-shaped media 10 are shifted in one direction with respect to the center of the hub 12; the center of the hub 12 is shifted in the opposite direction with respect to the center of the hub adaptor 14. With their eccentricity, the centers of the disk-shaped media 10 can be coincided with the rotational axis of the motor 16. However, if manufacturing accuracy of the disk-shaped media 10 is much lower than that of other members, the clearances cannot be absorbed. Namely, the centers of the disk-shaped media 10 cannot coincide with the rotational axis of the motor 16. Therefore, in the conventional method shown in FIGS. 5A and 5B, manufacturing accuracy of the disk-shaped media 10 and other members must be high.
As described above, in the conventional method shown in FIGS. 5A and 5B, the disk-shaped media are precisely positioned on the rotary shaft by using the amount of eccentricity.
However, in servo track writers of some magnetic disk drive units, the centers of the disk-shaped media merely coincide with the center of the hub. Then, the centers of the disk-shaped media are correctly positioned when they are assembled in the disk drive unit.
In the case of using a plurality of types of the disk-shaped media, inner diameters of the center holes are not fixed, so the conventional hub cannot be used. To overcome this problem, a new hub corresponding to the different types of the media must be prepared, or the conventional hub must be machined so as to correspond to the different types of the media.
However, preparing the new hub and machining the conventional hub are troublesome, so that manufacturing efficiency must be lower and manufacturing cost must be higher. Since the hub for the servo track writer must be machined precisely and it must be prepared for each servo track writer, preparing a new hub much increases the manufacturing cost.